1. Field of the Invention
The present invention relates to the field of medical imaging and more particularly the viewing of body organs under endoscopy during surgical operations.
2. State of the Art
Surgical endoscopy is a minimally invasive medical investigation technique which, whilst ensuring repair that is identical to conventional techniques, can reduce the size of incisions and limit regions of dissection. It is called laparoscopy for minimally invasive surgery via the abdominal cavity. This surgical technique considerably reduces operative trauma, risks of complications, pain and patient recovery time, and limits cosmetic impairment.
Endoscopy nonetheless remains difficult to carry out and requires specific learning procedures. For the surgeon, a direct view of the operative site is replaced by a 2D image on a monitoring screen via an endoscope, with the limitations this entails: imperfect illumination, shadowy regions, difficult perception of reliefs, limited field of vision, possible occlusions with instruments hidden by organs. This viewing system may contain geometric deformations and has limited resolution, contrast and colour.
Different three-dimensional (3D) viewing systems have therefore been developed to re-create perception of depth so as to improve visualization of body organs at the operative site.
The simplest and most economical solution to cause depth to appear in an endoscopic image is to create shadows. By adding indirect light in addition to the light source located at the end of the endoscope, it is possible to project shadows onto the viewed structures, thereby recreating a new sense of depth. Said viewing system gives poor performance however and does not provide satisfactory image quality for the practitioner.
Another solution consists of using a stereo-endoscope coupled with polarizing glasses. A stereo-endoscope consists of a single endoscope in which two separate optical systems are assembled and two cameras, allowing slightly different images to be captured of one same region, and thereby imitating human vision. The images given by the stereo-endoscope are then alternately projected onto a single screen at a frequency of 100 Hz. The screen is polarized vertically and then horizontally by an active polarizing filter. The polarizing glasses have one glass polarized vertically and another polarized horizontally so that each eye only receives one of these two images, thereby providing the surgeon with a 3D view of the region under observation. Nonetheless, this type of system comprises a certain number of disadvantages, related firstly to the stereo-endoscope, which only permits observations over very short distances, and secondly to the use of glasses which cause eye fatigue, which means that this solution can scarcely be used for operations which may last several hours. In addition, the image quality remains inferior to existing two-dimensional (2D) viewing systems.
A 3D endoscopic imaging system using structured light has also been developed. It consists of two channels, one allowing an image to be obtained, the other allowing projection of structured light. Light structuring consists of projecting light, generally a white light, through line arrays so as to create a frame on the object to be acquired. The object is viewed by a camera such as a CCD camera (charge coupled device) which observes the object through a slightly offset frame so as to create a Moiré effect. The distribution and intensity of this effect enhance the volume of the object and allow acquisition of the third dimension. However, said system is difficult to implement and above all it is costly.
In addition to the drawbacks already cited for each of the existing 3D viewing systems, these systems do not offer expected quality of viewing, some visual discomfort always being present. Since endoscopic surgery already entails major constraints, 2D viewing systems are more reliable, and therefore remain the preferred choice of surgeons despite the drawbacks related to their use.
Finally, most viewing tools for endoscopic surgery are relatively complex to use since, in addition to carrying out surgical movements, the practitioner must also move the endoscope in relation to the desired field of vision or give orders to an assistant to move the endoscope into the desired field of vision.
One purpose of the present invention is therefore to propose an endoscopic imaging system permitting three-dimensional viewing of an operative site, which is simple and is able to solve at least one of the above-cited disadvantages.